Excretion

Question 1

What is main organ for excretion?

Answer 1

Kidneys

Question 2

Name other routes of excretion ( 6)

Answer 2

1. Liver - into bile
2. GI tract
3. Lungs - gaseous anaesthetic
4. Sweat
5. Breast milk
6. Saliva

Question 3

What is enterohepatic reuptake

Answer 3

process whereby a drug or a metastable metabolite thereof in the liver is secreted into the bile, stored in the gall bladder, and subsequently released into the small intestine, where the drug can be reabsorbed back into circulation and subsequently returned to the liver.

Question 4

What is Clearance

Answer 4

Sum of all elimination routes
Cl total =cl kidney +cl liver + cl other routes

Question 5

What is clearance rate?

Answer 5

Amount of drug leaving body in a given time

Question 6

Name factors for renal excretion? (7)

Answer 6

1. Water soluble
2. Small enough to fall through kidney glomerulus perforations
3. Don’t rapidly diff into lipid membranes
4. Present in significant quantities in blood/ plasma/ extra cellular fluid ( high vol distribution)
5. Maybe filtered reabsorbed or excreted
6. Depends on good kidney function
7. Nutrients like glucose- filtered then quickly reabsorbed so not wasted

Question 7

Factors for biliary excretion

Answer 7

1. Maybe water sol and too big to pass through glomerular
2. Maybe too lipophilic to be filtered without being reabsorbed again
3. Some drugs transformed by metabolic processes
4. Some excreted without being charged eg erythromycin or rifampicon
5. Some enterohepatic reuptake - steroids, oral contraceptives

Question 8

What is zero order excretion?

Answer 8

Rate of excretion of drug independent of its concentration

Can’t be influenced
Only few drugs eg ethanol- basis of breathalyser test
Phenytoin , fluoxetine, omeprazole

Plot of drug conc vs time - linear
Non linear kinetics

Question 9

What is first order excretion

Answer 9

Rate of excretion directly proportional to its concentration

Most drugs

Plot of drug conc vs time is linear - linear kinetics

Question 10

What is glomerular filtration

Answer 10

passive process that your kidneys use to filter excess fluid and waste products out of the blood into the urine collecting tubules of the kidney, so they may be eliminated from your body
Depends on hydrostatic pressure
Measure by GFR
( normal above 90 but probably ok over 50

Question 11

What is tubular secretion

Answer 11

is the transfer of materials from capillaries to the renal tubular lumen

Often requires energy
Lipid sol ( un ionised drugs) - passive diffusion ie reabsorbed into bloodstream

Ionised will stay in urine